Implement safe shell reloading inside omf plugin

This commit adds an improved reload code for Oh My Fish, besides
saving the history now the reloading technique keeps directory
history and stack and clears fish_greeting, for a transparent
transition.

The reloading code is now safe regarding to background jobs. exec
wipes fish job control, so the user-facing code under the (just-
introduced by this commit) `omf reload` command is kept safe by a
warning. For testing purposes, `omf update` and `omf remove` rolls
automatic refresh only when `OMF_AUTO_RELOAD` variable is set.

Recap of the commit:
- Add improved reload code (omf.reload)
- Add a safe reload code (omf.cli.reload)
- Add `omf reload` command
- Add opt-in reload to `omf update` and `omf remove` commands

Add ru-RU docs

`omf doctor` checks for fish & git versions

Minimum fish version: 2.2.0
Minimum git version: 1.9.5

lib: deprecate `refresh` function

lib: deprecate `available` function

This PR officially marks available as deprecated, moving the
deprecated functionality to omf plugin compat quarantine directory.

With great power comes great responsibility. This function is
somewhat low level, and is harmful to shell's user, as it
completely screws up with job control (subprocesses).

This PR officially marks `refresh` as deprecated, moving the
deprecated functionality to omf plugin `compat` quarantine
directory.

Add hash plugin to database

Add ssh-config.d plugin into database

registry: point direnv plugin to organization's version

Add expand plugin to database

Add argu plugin to database

Create mars

Add termux plugin to database

Update plugin URLs and remove broken plugin entries

Allow selective updates

Add phpbrew plugin to database

registry: remove deprecated agnoster-mercurial theme

Improve OMF CLI completions

docs: update Themes.md